Lashes could be a great deal of trouble (6)
I believe the answer is:
hassle
'a great deal of trouble' is the definition.
'hassle' can be an answer for 'trouble' (synonyms). I'm not certain of the 'a great deal of' bit.
'lashes could be' is the wordplay.
'could be' indicates anagramming the letters.
'lashes' with letters rearranged gives 'HASSLE'.
Can you help me to learn more?
(Other definitions for hassle that I've seen before include "Pester or annoy" , "Informally annoy or bother" , "problem" , "Irritating inconvenience" , "Harass; pester" .)